ANATOMY AND PHYSIOLOGY 



the external air; the quantity of inspired oxygen in- 

 creases with the loss of heat by external cooling, and 

 the quantity of carbon or hydrogen necessary to com- 

 bine with this oxygen must be increased in like ratio. 

 It is evident that the supply of heat lost by cooling is 

 effected by the mutual action of the elements of the 

 food and the inspired oxygen, which combine together. 

 To make use of a familiar, but not on that account 

 a less just illustration, the animal body acts, in this 

 respect, as a furnace, which we supply with fuel. It 

 signifies nothing what intermediate forms food may 

 assume, what changes it may undergo in the body, 

 the last change is uniformly the conversion of carbon 

 into carbonic acid and of its hydrogen into water ; the 

 unassimilated nitrogen of the food, along with the un- 

 burned or unoxidized carbon, is expelled in the ex- 

 cretions. In order to keep up in a furnace a constant 

 temperature, we must vary the supply of fuel accord- 

 ing to the external temperature that is, according to 

 the supply of oxygen. 



"In the animal body the food is the fuel; with a 

 proper supply of oxygen we obtain the heat given out 

 during its oxidation or combustion." 8 



BLOOD CORPUSCLES, MUSCLES, AND GLANDS 



Further researches showed that the carriers of oxy- 

 gen, from the time of its absorption in the lungs till its 

 liberation in the ultimate tissues, are the red corpuscles, 

 whose function had been supposed to be the mechan- 

 ical one of mixing of the blood. It transpired that 

 the red corpuscles are composed chiefly of a substance 

 which Kuhne first isolated in crystalline form in 1865, 



VOL. iv.-io 



